Field of the Invention
The invention relates to a method and an apparatus for smear-free guidance of a printed sheet on a sheet-guiding cylinder of a printing press, in particular, on a turning drum of a sheet-fed rotary offset printing press in first-form or recto sheet printing mode, wherein a leading edge of a sheet is taken over by a gripper device of the sheet-guiding cylinder from a sheet-guiding cylinder preceding or located up-line from the latter.
In the field of sheet-fed rotary offset printing presses, there is a problem that, when sheets are transported through the printing press, the freshly printed side thereof come into contact with the circumferential surfaces of the transfer cylinders transporting them, thereby smearing the printed image in contact with the circumferential surface. To avert smearing of the freshly printed image, various methods have become known heretofore in the prior art for guiding a printed sheet in a smear-free manner on the circumferential surface of a printing press cylinder.
It has become known heretofore, for example, from European Patent 0 059 944 to slip over a sheet-guiding cylinder an ink-repelling net which is easily movable on the surface of the cylinder, in order to prevent smearing of a freshly printed page of the sheets.
It has also become known heretofore from the Published, Non-prosecuted German Patent Application (DE-OS) 195 46 311 A1 to equip a sheet transfer drum with inflatable jacket segments formed with openings in the surface thereof out of which air flows so as to produce a supporting air film for holding the sheet on the transfer drum.
The problem of smearing a freshly printed upper side of a sheet on the circumferential surface of turning drums of sheet-fed rotary printing presses having a turning device occurs in a similar manner, if these presses are operated at a high printing speed in a first-form or recto sheet printing mode.
Such a printing press with a sheet-turning device having a turning drum has become known heretofore, for example, from German Patent DE 30 50 295, wherein a sheet, in a first-form or recto sheet printing mode, is taken over by a tongs-type gripper of the turning drum from a preceding or up-line storage drum and, thus, a freshly printed upper side of the sheet comes into contact with the circumferential surface of the turning drum. It has also become known from this German patent to fix the sheet at the trailing edge thereof by suction cups to the circumferential surface of the storage drum.